Transducers in the form of electrode arrays are known in the prior art for various purposes. In general, and for the purpose of this invention, an electrode array is a circular arrangement of electrodes or an arrangement of electrodes which is symmetrical about a center point which electrodes are printed or etched onto a carrier plate. A drive signal of some type is provided to the electrodes in the array. Additionally, the center point includes a center reading or detecting electrode.
One specific example with which the present invention is particularly adapted for use is described in U.S. Pat. No. 4,007,454. A description of an improved version of the electrode array for the aforesaid patent is described in patent application Ser. No. 728,119, filed Sept. 20, 1976 and now U.S. Pat. No. 4,429,308 issued Jan. 31, 1984. In each of these patents, there is provided a plurality of drive electrodes arranged in a symmetrical pattern about a center reading electrode. A drive signal is transmitted to each electrode, and coupled to the center electrode to form an electric field of known characteristics. By placing the electrode array in confronting relation to a rotating member which is immersed in the electric field its position can be detected. In the absence of any disturbance in the field adjacent the array, the signal on the center electrode is zero. However, in the presence of a meter hand or some other imbalance creating situation, an imbalance will be created which can be detected at the center electrode, and a signal representative of the imbalance will be generated.
The problem then exists as to how to get the electrical signal from an electrode in the center of the array to some contact point outside the electrode array from which the signal can be operatively utilized. According to a first approach, a hole was drilled through the center electrode, and a wire attached to the rear thereof or to a post mounted in the rear thereof. The wire then became the conductive path for the signal from the center electrode. This technique proved to be expensive, and difficult to accomplish because of the fragility of the carrier plate upon which the electrodes are deposited. Further, the wire from the center electrode introduced an inherent perturbation or disturbance, and therefore extreme care had to be taken to properly shield the output line. As a result, this approach was determined to be impractical.
While it might appear that a conductive path could be deposited or printed onto the face of the transducer plate, which conductive path or strip would extend between two of the electrodes, it quickly becomes apparent that this approach is unsatisfactory, because it also introduces inadvertent imbalances in the electric field that produce an erroneous signal on the center electrode. The critical balance of the electric field from the surrounding electrodes on the center electrode and its extension(s) must be maintained or else the output signal becomes unusable.
In accordance with the present invention, there is provided a means for satisfactorily transferring the detected signal from the center electrode to a point outside the electrode array without causing signal imbalances on the center electrode due to unbalanced drive signal coupling to the center electrode. Toward this end, one conductive path, strip or arm is deposited on the face of the plate which extends from the center electrode between two adjacent electrodes and out to a contact point. Other secondary conductive arms are deposited on the face of the transducer plate which extend from the center electrode through each of the openings between the other electrodes, so that every opening between electrodes carries a conductive strip. These secondary strips terminate substantially minimally co-extensive with the radial extremities of the electrodes, as it is not necessary to carry them further. That is to say that the strips should not terminate in the area between two electrodes, although they can extend beyond the radial extremities of the adjacent electrodes. Such an arrangement has been proven to not generate extraneous signal imbalances on the center electrode, and the output signal maintains its accuracy.
While the background and summary of the invention have been described in connection with a transducer which generates an electric field surrounding an electrode array which field immerses a meter hand, the position of which is to be detected, there are potentially other electrode arrays with which the present invention is adapted for use. Further, while in the embodiment to be illustrated and described there is only one conductive path from the center electrode to the contact point, it is also possible that other arrangements could be utilized in which two or more conductive paths are live and extend all the way from the center electrode to one or more contact points.
It is therefore an object of the present invention to provide a means whereby an electrical signal can be transmitted from a center electrode which is itself deposited upon a transducer plate substantially at the center of an array of drive electrodes to a point outside the array without causing extraneous imbalances in the signal on the center electrode.